1. Field of the Invention
The present invention relates to a semiconductor device including a driver and a matrix circuit, and more particularly to the semiconductor device which reduces a possible off current flowing through each of thin film transistors which constitutes a part of the matrix circuit.
2. Description of the Related Art
FIG. 6 shows one example of a conventional thin film transistor, which includes a substrate 1, for example, of glass, and a semiconductor film 2 formed at a predetermined position on an upper surface of the substrate 1. The semiconductor film 2 has a channel 2a at its central portion with a source and a drain region 2b at the corresponding side portions of the film 2 excluding the channel 2a. A gate insulation film 3 is formed on the whole surface of the substrate 1 and the semiconductor film 2. A gate electrode 4 is formed on an upper surface of that portion of the gate insulation film 3 corresponding to the channel region 2a. An inter-layer insulation film 5 is formed on the whole surface of the gate insulation film 3 and the gate electrode 4. Contact holes 6 are formed in those parts of the inter-layer insulation film 5 and gate insulation film 3 corresponding to the source and drain regions 2b. Source and drain electrodes 7 are formed in the corresponding contact holes 6 and at a predetermined position on the inter-layer film 5.
When the gate electrode 4 of an NMOS thin film transistor of the above structure had a width of 60 .mu.m and a length of 6 .mu.m, the transistor exhibited the V.sub.G (gate voltage)-I.sub.D (drain current) characteristic of FIG. 7. As is clear in FIG. 7, when the drain voltage V.sub.D was 1 or 5 V, the on/off current ratio was large, for example, on the order of a number of seven figures, and showed that the characteristic was excellent. The off current, however, was 10.sup.-11 A when the drain voltage V.sub.D was 1 V, and 10.sup.-10 A when the drain voltage V.sub.D was 5 V, i.e., the off current was relatively large.
That is, there is the problem with the conventional thin film transistor that the off current and hence the leakage current are relatively large.